1. Field of the Invention
The present invention relates to a semiconductor device, more particularly to a semiconductor device that outputs a pulse waveform with reduced electromagnetic interference.
2. Description of the Related Art
Semiconductor devices need to be able to operate without producing excessive electromagnetic interference (EMI), and at the same time their electromagnetic susceptibility (EMS), that is their tendency to malfunction in the presence of external electromagnetic interference, needs to be low. A known output buffer circuit (see Japanese Patent Application Publication No. 2002-57566) meets these conflicting requirements by adding a control circuit to a bi-level output circuit. The bi-level output circuit outputs a signal having a pulse waveform with a high voltage level and a low voltage level. The control circuit reduces the driving ability of the bi-level output circuit during transitions of the output signal between these two levels, as compared with the driving ability when the output signal is being maintained at one level or the other.
The addition of the control circuit, however, makes this output buffer circuit problematically complex. Specifically, the control circuit must detect signal transitions and output various driving signals with different timings.